62 Chevy 235 in my wife's 53 Chevy is giving me a fit. Running rough, has Langdon hei, and carb on a stock intake. Has split exhaust run out the back shotgun style. Front cylinder has good spark but plug is wet. The exhaust is noticeably cooler on one of the tailpipes and drawing a slight vacuum when covered with my palm. HELP!
It sounds like it’s time for a compression test. You are not necessarily looking for an exact number, but they should all be even. If you find a cylinder with lower compression than the others, put a few squirts of oil in the spark plug hole and retest, if the number increases, likely the rings are worn out. If it stays the same, it’s a holed piston or a valve/valve train problem.
Do you have the correct coil, plugs and plug gap? The HEI needs a hotter coil and a wider gap on the correct extended tip plugs. The HEI is a great swap and is usually trouble free. Also, the carb may need to be adjusted?
Something I have learned about HEIs and electronic ignition in general. They can do weird shit. The control mod or even the pick up coil does not always completely leave the building. If it is a GM style HEI you may take a look at the reluctor (SP?) and see that it is not bent or maimed in some fashion. Tell you a story (one that is still fresh in my head). A few years back I went to troubleshoot an SBC in a friends car. When you fired it off it would run normal until it got to about 160 degrees then it would run like a governed stationary motor. Brrrrrrmmm, Brrrrrrmm, Brapp brapp and etc. They had already tried everything with it. It had a brandy new Accel electronic. I said, easy the only thing that could be is the distributer. Pulled it took it to a distributer shop to be checked, it checked out perfect. Put it back in, ran a simple tune up including adjusting the valves (which I thought were a little tight and I addressed that matter). Finally out of pure desperation I jerked the distributer out of my pickup and dropped it in. Ran perfect with my distributer. Try a different distributer then go back to pulling your hair out.
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